Höfle et al. describe the cytotoxic action of the natural substances epothilone A (R=hydrogen) and epothilone B (R=methyl) of the following formula:
in, e.g., Angew. Chem. [Applied Chem.], 1996, 108, 1671–1673. Because of their in-vitro selectivity for breast cell lines and intestinal cell lines and their significantly higher activity against P-glycoprotein-forming multiresistant tumor lines in comparison to taxol as well as their physical properties that are superior to those of taxol, e.g., a water solubility that is higher by a factor of 30, this novel structural class is especially advantageous for the development of a pharmaceutical agent for treating malignant tumors.
The natural substances are not sufficiently stable either chemically or metabolically for the development of pharmaceutical agents. To eliminate these drawbacks, modifications to the natural substance are necessary. Such modifications are possible only with a total-synthesis approach and require synthesis strategies that make possible a broad modification of the natural substance. The purpose of the structural changes is also to increase the therapeutic range. This can be done by improving the selectivity of the action and/or increasing the active strength and/or reducing undesirable toxic side-effects, as they are described in Proc. Natl. Acad. Sci. USA 1998, 95, 9642–9647.
The total synthesis of epothilone A is described by Schinzer et al. in Chem. Eur. J. 1996, 2, No. 11, 1477–1482 and in Angew. Chem. 1997, 109, No. 5, pp. 543–544). Epothilone derivatives were already described by Höfle et al. in WO 97/19086. These derivatives were produced starting from natural epothilone A or B. Also, epothilones C and D (double bond between carbon atoms 12 and 13: epothilone C=deoxyepothilone A; epothilone D=deoxyepothilone B) are described as possible starting products for this purpose.
Another synthesis of epothilone and epothilone derivatives was described by Nicolaou et al. in Angew. Chem. 1997, 109, No. 1/2, pp. 170–172. The synthesis of epothilone A and B and several epothilone analogues was described in Nature, Vol. 387, 1997, pp. 268–272; and the synthesis of epothilone A and its derivatives was described in J. Am. Chem. Soc., Vol. 119, No. 34, 1997, pp. 7960–7973 as well as the synthesis of epothilone A and B and several epothilone analogues in J. Am. Chem. Soc., Vol. 119, No. 34, 1997, pp. 7974–7991 also by Nicolaou et al.
Nicolaou et al. also describe in Angew. Chem. 1997, 109, No. 19, pp. 2181–2187 the production of epothilone A analogues using combinative solid-phase synthesis. Several epothilone B analogues are also described there.
Epothilone derivatives, in some cases also epothilone C and D, are also described in patent applications WO 99/07692, WO 99/02514, WO 99/01124, WO 99/67252, WO 98/25929, WO 97/19086, WO 98/38192, WO 99/22461 and WO 99/58534.
In the epothilone derivatives previously known, no alkenyl, alkinyl or epoxy radical was provided on carbon atom 6 (see the above formula) of the epothilone skeleton.